Motorcycle enthusiasts number in the hundreds of thousands. Many riders, especially those who enjoy long-distance touring, prefer the power and stability of large touring bikes. To gain additional stability and load-carrying capacity, a sizeable minority have opted to convert their two-wheeled motorcycles to three-wheeled vehicles, or “trikes.”
In such a conversion most of the systems of the motorcycle are typically retained except for the rear portions of the drive train, the rear suspension, and the rear brake system. However, since the handling characteristics of a three-wheeled vehicle are very different than those of a two-wheeled vehicle, some modifications are needed to allow safe and comfortable operation of the vehicle.
Safe and effective modifications to the brake system are especially critical. Motorcycles have traditionally employed a foot pedal to actuate the rear brake and a hand lever to actuate the front brake. In motorcycles with hydraulic braking systems, the foot pedal and the hand lever each actuate a different master cylinder.
Since a motorcycle tends to pitch forward when braking, placing more downward, friction-producing force on the front wheel, skilled operators usually apply more braking pressure to the front wheel than to the rear wheel. However, relatively unskilled motorcycle operators often instinctively rely too heavily on the rear brake to stop the motorcycle, resulting in an uncontrolled skid. To provide safe and effective braking regardless of operator misjudgment, some motorcycle manufacturers have equipped their products with braking systems that link the front and rear brakes with control systems that allocate the optimum amount of braking pressure to each wheel no matter which master cylinder is actuated.
Linked braking systems on motorcycles usually allocate more braking pressure to the front wheel. Unfortunately, that pressure allocation is usually not suitable for a trike. The trike, of course, has two wheels in the rear. Those rear wheels are usually larger than the rear wheel of a motorcycle, resulting in more road contact area and braking friction. Also, a trike often carries more weight in the rear in the form of passengers and luggage. Diverting extra braking pressure to the front wheel of a trike may result in ineffective and erratic braking and may in some cases destabilize the vehicle.
Some modification to the braking system of a trike conversion is clearly needed, but since modifications to the original motorcycle brake master cylinders and control systems are both cost-prohibitive and likely to raise complex engineering and safety issues, most modifications known in the art have relied on various ways of connecting, disconnecting, or redirecting the master cylinder outputs.
In one known modification the outputs from the front and rear master cylinders are directly connected. This modification provides no ability to optimize the front-to-rear braking pressure allocation and often produces an odd “feel” to the brake foot pedal, causing the pedal to “drop” and the trike to roll backward slightly once the vehicle has stopped and the braking pressure has eased.
In another known modification, one master cylinder is simply disconnected and remaining master cylinder (usually the rear) is used to drive the entire braking system. This modification allows more even pressure distribution, but greatly reduces available braking force and user control while still providing no effective means for optimizing braking pressure distribution.
Still another approach is to direct all hand lever brake pressure to the front brake and all foot pedal brake pressure to the rear brake. Although this approach preserves available braking pressure and operator control, it negates the safety features provided by linked control systems.
What is needed is a simple, safe, and inexpensive motorcycle brake system modification for motorcycle conversions that preserves the advantages of the motorcycle's original linked braking control systems, requires no changes to the original master cylinders or front braking systems, and provides a means for optimizing the front-to-rear allocation of braking pressure.
The present invention provides such a modification. A preferred embodiment of the present invention comprises a disc brake caliper that integrates two or more separate sets of opposed braking cylinders and pads within a single housing. Braking cylinder sets are not connected to other braking cylinder sets within the housing. Each set of braking cylinders is connected to and actuated independently by a different master cylinder.
The amount of braking pressure exerted by a braking cylinder set is proportional to diameter of the cylinders in the set. In a preferred embodiment of the present invention, at least two braking cylinder sets within a housing have different diameters, the diameters of each set being chosen to produce a desired amount of braking pressure in response to an expected amount of hydraulic pressure from the master cylinder actuating the set. Both the diameter of each braking cylinder set and ratio of diameters between different braking cylinder sets are chosen to produce the optimum rear wheel braking pressure allocation for a given braking control system and vehicle configuration, with no changes to the master cylinders or the front wheel braking system.